In some current 3G, Wimax and LTE (Long Term Evolution) radio access networks, the base station is configured as a concentrated node with essentially most of the components being located at concentrated site. However, a radio base station can also be configured with a more distributed architecture. For example, a distributed radio base station can take the form of one or more radio equipment (RE) portions that are linked to a radio equipment control (REC) portion over a radio base station internal interface.
FIG. 1 is a schematic diagram illustrating the internal connections inside the radio base station. The radio base station includes a REC and a RE, with a radio base station internal interface shown as CPRI (Common Public Radio Interface) which connects the REC and the RE. The Common Public Radio Interface (CPRI) is described in Common Public Radio Interface (CPRI) Interface Specification Version 3.0 (Oct. 20, 2006), which is incorporated herein by reference. The interface between the REC and RE may also include, for example, Open Base Station Architecture Initiative (OBSAI), Ir (an interface between a base band unit (BBU) and a remote radio unit (RRU)), etc.
The CPRI is typically implemented on optical fiber and currently supports maximum line bit rate of 2.4576 Gbps. With rapid development of mobile communication service, the amount of data as transferred between the REC and RE are increasing dramatically. For example, operators like China Mobile now requires a TD-SCDMA (time division synchronous code division multiple access) base station with maximum capacity of 192A×C (A=antenna and C=carrier), or a LTE base station with 20 MHz bandwidth and 8 antennas. For such a base station, it is required to transfer roughly 9 Gbps data between a REC and a RE for transmission and reception respectively. Take a LTE base station with 20 MHz bandwidth and 8 antennas as an example. For the baseband sampling rate 30.72 MHz/s in LTE standard, normally, IQ (including the real part and the imaginary part) bit width is 16 bits, after passing through the 8 B/10 B encoder for clock recovery and line DC balance defined in CPRI and Ir physical layer, the data rate is 1.2288 Gbps for one antenna. The total Tx or Rx data rate for 8 antennas is 1.2288 Gbps*8=9.8304 Gbps. Therefore, the LTE base station needs four 2.4576 Gbps CPRI links, physically, 4 fibers between the REC and one RE, in order to support 8 antennas data.
In a typical deployment as shown in FIG. 2, one REC may be connected with 3 REs, which means 12 fibers are need for data transmission there between. Large number of fibers may lead to high cost on construction and maintenance as well.